/*
 * Copyright (C) 2011 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.primitives;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.primitives.UnsignedInts.INT_MASK;
import static com.google.common.primitives.UnsignedInts.compare;
import static com.google.common.primitives.UnsignedInts.toLong;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import java.math.BigInteger;
import javax.annotation.Nullable;

/**
 * A wrapper class for unsigned {@code int} values, supporting arithmetic operations.
 *
 * <p>
 * In some cases, when speed is more important than code readability, it may be faster simply to
 * treat primitive {@code int} values as unsigned, using the methods from {@link UnsignedInts}.
 *
 * <p>
 * See the Guava User Guide article on
 * <a href="https://github.com/google/guava/wiki/PrimitivesExplained#unsigned-support">unsigned
 * primitive utilities</a>.
 *
 * @author Louis Wasserman
 * @since 11.0
 */
@GwtCompatible(emulated = true)
public final class UnsignedInteger extends Number implements Comparable<UnsignedInteger> {
    public static final UnsignedInteger ZERO = fromIntBits(0);
    public static final UnsignedInteger ONE = fromIntBits(1);
    public static final UnsignedInteger MAX_VALUE = fromIntBits(-1);

    private final int value;

    private UnsignedInteger(int value) {
        // GWT doesn't consistently overflow values to make them 32-bit, so we need to force it.
        this.value = value & 0xffffffff;
    }

    /**
     * Returns an {@code UnsignedInteger} corresponding to a given bit representation. The argument
     * is interpreted as an unsigned 32-bit value. Specifically, the sign bit of {@code bits} is
     * interpreted as a normal bit, and all other bits are treated as usual.
     *
     * <p>
     * If the argument is nonnegative, the returned result will be equal to {@code bits}, otherwise,
     * the result will be equal to {@code 2^32 + bits}.
     *
     * <p>
     * To represent unsigned decimal constants, consider {@link #valueOf(long)} instead.
     *
     * @since 14.0
     */
    public static UnsignedInteger fromIntBits(int bits) {
        return new UnsignedInteger(bits);
    }

    /**
     * Returns an {@code UnsignedInteger} that is equal to {@code value}, if possible. The inverse
     * operation of {@link #longValue()}.
     */
    public static UnsignedInteger valueOf(long value) {
        checkArgument((value & INT_MASK) == value, "value (%s) is outside the range for an unsigned integer value",
                value);
        return fromIntBits((int) value);
    }

    /**
     * Returns a {@code UnsignedInteger} representing the same value as the specified
     * {@link BigInteger}. This is the inverse operation of {@link #bigIntegerValue()}.
     *
     * @throws IllegalArgumentException if {@code value} is negative or {@code value >= 2^32}
     */
    public static UnsignedInteger valueOf(BigInteger value) {
        checkNotNull(value);
        checkArgument(value.signum() >= 0 && value.bitLength() <= Integer.SIZE,
                "value (%s) is outside the range for an unsigned integer value", value);
        return fromIntBits(value.intValue());
    }

    /**
     * Returns an {@code UnsignedInteger} holding the value of the specified {@code String}, parsed
     * as an unsigned {@code int} value.
     *
     * @throws NumberFormatException if the string does not contain a parsable unsigned {@code int}
     *         value
     */
    public static UnsignedInteger valueOf(String string) {
        return valueOf(string, 10);
    }

    /**
     * Returns an {@code UnsignedInteger} holding the value of the specified {@code String}, parsed
     * as an unsigned {@code int} value in the specified radix.
     *
     * @throws NumberFormatException if the string does not contain a parsable unsigned {@code int}
     *         value
     */
    public static UnsignedInteger valueOf(String string, int radix) {
        return fromIntBits(UnsignedInts.parseUnsignedInt(string, radix));
    }

    /**
     * Returns the result of adding this and {@code val}. If the result would have more than 32
     * bits, returns the low 32 bits of the result.
     *
     * @since 14.0
     */
    public UnsignedInteger plus(UnsignedInteger val) {
        return fromIntBits(this.value + checkNotNull(val).value);
    }

    /**
     * Returns the result of subtracting this and {@code val}. If the result would be negative,
     * returns the low 32 bits of the result.
     *
     * @since 14.0
     */
    public UnsignedInteger minus(UnsignedInteger val) {
        return fromIntBits(value - checkNotNull(val).value);
    }

    /**
     * Returns the result of multiplying this and {@code val}. If the result would have more than 32
     * bits, returns the low 32 bits of the result.
     *
     * @since 14.0
     */
    @GwtIncompatible // Does not truncate correctly
    public UnsignedInteger times(UnsignedInteger val) {
        // TODO(lowasser): make this GWT-compatible
        return fromIntBits(value * checkNotNull(val).value);
    }

    /**
     * Returns the result of dividing this by {@code val}.
     *
     * @throws ArithmeticException if {@code val} is zero
     * @since 14.0
     */
    public UnsignedInteger dividedBy(UnsignedInteger val) {
        return fromIntBits(UnsignedInts.divide(value, checkNotNull(val).value));
    }

    /**
     * Returns this mod {@code val}.
     *
     * @throws ArithmeticException if {@code val} is zero
     * @since 14.0
     */
    public UnsignedInteger mod(UnsignedInteger val) {
        return fromIntBits(UnsignedInts.remainder(value, checkNotNull(val).value));
    }

    /**
     * Returns the value of this {@code UnsignedInteger} as an {@code int}. This is an inverse
     * operation to {@link #fromIntBits}.
     *
     * <p>
     * Note that if this {@code UnsignedInteger} holds a value {@code >= 2^31}, the returned value
     * will be equal to {@code this - 2^32}.
     */
    @Override
    public int intValue() {
        return value;
    }

    /**
     * Returns the value of this {@code UnsignedInteger} as a {@code long}.
     */
    @Override
    public long longValue() {
        return toLong(value);
    }

    /**
     * Returns the value of this {@code UnsignedInteger} as a {@code float}, analogous to a widening
     * primitive conversion from {@code int} to {@code float}, and correctly rounded.
     */
    @Override
    public float floatValue() {
        return longValue();
    }

    /**
     * Returns the value of this {@code UnsignedInteger} as a {@code float}, analogous to a widening
     * primitive conversion from {@code int} to {@code double}, and correctly rounded.
     */
    @Override
    public double doubleValue() {
        return longValue();
    }

    /**
     * Returns the value of this {@code UnsignedInteger} as a {@link BigInteger}.
     */
    public BigInteger bigIntegerValue() {
        return BigInteger.valueOf(longValue());
    }

    /**
     * Compares this unsigned integer to another unsigned integer. Returns {@code 0} if they are
     * equal, a negative number if {@code this < other}, and a positive number if
     * {@code this > other}.
     */
    @Override
    public int compareTo(UnsignedInteger other) {
        checkNotNull(other);
        return compare(value, other.value);
    }

    @Override
    public int hashCode() {
        return value;
    }

    @Override
    public boolean equals(@Nullable Object obj) {
        if (obj instanceof UnsignedInteger) {
            UnsignedInteger other = (UnsignedInteger) obj;
            return value == other.value;
        }
        return false;
    }

    /**
     * Returns a string representation of the {@code UnsignedInteger} value, in base 10.
     */
    @Override
    public String toString() {
        return toString(10);
    }

    /**
     * Returns a string representation of the {@code UnsignedInteger} value, in base {@code radix}.
     * If {@code radix < Character.MIN_RADIX} or {@code radix > Character.MAX_RADIX}, the radix
     * {@code 10} is used.
     */
    public String toString(int radix) {
        return UnsignedInts.toString(value, radix);
    }
}
